An adult mite is smaller than the head of a pin. It is only 0.5-1 mm in length. If you want to examine the mites properly you will have to use a strong magnifying glass.

Although they are referred to as red spider mites, in spring and summer they are actually light green, with two dark spots on the body. For this reason they are becoming known as the Two Spot Spider Mite.

The red spider mite sucks sap and, because of its large numbers, can seriously debilitate the plant. The affected plant part may look healthy. But on very close examination, you may see the tell-tale webbing, which appears on the undersides and in the axils of leaves. Tiny spots also appear on the leaves, creating a mottled effect on their surface. A really serious attack involves quite extensive yellowing, bronzing or leaf-fall.

Frost-tolerant pests

The red spider mite is quite hardy and can survive extremes of temperature. The hibernating female, especially, can live through hard frosts. Red spider mites usually appear in the autumn when the days become shorter and colder. At this stage they can happily survive temperatures as low as –10°C (14°F). They not only survive the cold, however; they also love dry air. The drier it is, the better their chances of thriving.

Their almost reddish-orange colouring. They emerge from hibernation in the spring and lay their eggs. At normal room temperatures the eggs will hatch in about three weeks. However, if the temperature is higher, up to 35°C (95°F) behind a sunny window — hatching will only take six days.

Dealing with an attack of red spider mite

If you discover an attack in time, a chemical insecticide may be the answer. You can use liquid derris extract or malathion, but follow the instructions on the label very carefully. However, in time the red spider mite will develop a resistance to the chemical, and eventually it may be of no use whatsoever. An alternative is to use predatory mites which will destroy the red spider

In the case of a major attack it is often too late to do anything. The only sensible action is to get rid of the plant as quickly as possible to prevent the mite spreading to other plants.

Disinfecting

After disposing of infected plants, it is important to clean and disinfect the area where the plant stood. Wash the saucers, pots and walls or windowsill carefully so that subsequent plants will not be affected. In future, make sure you check your plants regularly for early signs of infestation.

Biological Control

The most effective means of controlling red spider mite is to use biological control. This comes in the form of predatory mites which devour the pest. However, they are only really effective when used in a greenhouse.

The predatory mites are put on to the plants in early spring, before the red spider mites come Out of hibernation. They arc introduced gradually at 2-3 week intervals, so that they can spread from plant to plant and give sufficient cover by the time the red spider mite becomes active. This means of controlling the pest is not effective once an attack is underway.

Several firms in the UK supply predatory mites (in multiples of 1000). Details can be got from the Ministry of Agriculture.

Deterring an attack

The fact that red spider mites thrive in dry conditions provides you with the best weapon for deterring an attack. Maintain a high humidity around your plants by misting them during the daylight hours, and standing your plants on moist pebbles.

These mites abhor moist air and will not thrive or multiply in it. As well as misting regularly, put your larger plants under the shower to wash any mites away and stand them outside in the milder months during a gentle rainfall.

In addition, thoroughly clean your greenhouse, porch, conservatory and other areas where you keep plants, at least once a year. The best time to do [his is in the spring or autumn.

Make up a mild solution of disinfectant to wash down walls, shelving and floors. If you have double glazing, wash between the layers This can be an effective deterrent. If you are thorough, you reduce the chance of an attack. Make certain you wash in the corners and wash around any handles or hooks as well.

Do’s and Don’ts

Look at the undersides of the leaves for webbing, and use a magnifying glass to look for the mites themselves.

Remember to wash down areas around your plant frequently; the females may lay their eggs on windowsills or shelves.

DON’T

Forget to keep the air around your plant moist. Standing it on a tray of moist pebbles is one of the most effective ways of doing this. However you should also mist the plant or stand it under a gentle fall of water every so often, particularly in hot, dry weather.

Try to save a plant that has a serious attack of spider mite. Discard it.

Red spider mites can appear on almost any type of house plant.

Good hygiene and proper growing conditions help to prevent an attack, but if one occurs, take prompt action.